1. Field of the Invention
The present invention relates to a speed changing apparatus of bicycles, and particularly to a speed changing apparatus of bicycles, which assists gear shifting operation of the apparatus disposed in a rear wheel hub of the bicycle, thereby facilely shifting gears of the apparatus even with small force.
2. Description of Related Art
Generally, a bicycle run by force applied to a pedal has a speed changing apparatus in order to change rotational speed of wheels of the bicycle. As a speed changing apparatus of bicycles, there is an outer chain-type transmission including multiple sprockets which are disposed at a rear wheel and on which a chain is installed, and a derailer which selectively couples the chain with one of the sprockets.
In the outer chain-type transmission, there is a problem that the chain is frequently taken off from the sprockets during running of the bicycle and thus should be reinstalled on the sprockets. Herein, since lubricating oil such as grease is applied on the chain so that the chain can be facilely moved, the lubricating oil may be stained on rider's clothes, and the hands are also smeared with the lubricating oil while reinstalling the taken off chain. Further, in case that the rider is a woman or a child, it is difficult to reinstall the taken off chain on the sprocket.
In order to solve the problems in the outer chain-type transmission, there has been recently proposed an inner gear-type transmission which is disposed in the rear wheel hub. As an example of the inner gear-type transmission, there has been disclosed an apparatus for changing speed of bicycles (Korean Patent No. 10-0436697) which had proposed by the inventor.
The apparatus for changing speed of bicycles above-mentioned, as shown in FIG. 1, includes a driven sprocket 100 for receiving the driving force of a driving sprocket; a speed controlling portion including a carrier 210 fixed to one side of the driven sprocket 100 and having a plurality of planetary gears 220 installed thereon, two or more sun gears 231 and 232 each having ratchet-teeth being formed along its inner circumference, and a ring gear 240 engaged with the planetary gears 220; an output portion including a hub shell 310 for transferring driving force to a rear wheel of a bicycle by means of the carrier 210 and the ring gear 240, and clutch means 320 mounted between the carrier 210 and the hub shell 310 and the ring gear 240 and the hub shell 310 to selectively transmit the driving force; and a speed-changing controlling portion including a hub shaft 410 having a pawl positioning portion 411, two or more pawls 421 and 422 operative to be engaged with or disengaged from the ratchet-teeth of the two or more sun gears 231 and 232, a pawl-controlling ring 430 operative to control positions of the pawls 421 and 422, a transforming disk 450 having a groove for winding a wire along its outer circumference and a hooking portion on the outer circumference, the transforming disk being operative to transform a position of the pawl-controlling ring 430 via a mediating portion 440, a spring 460 for restoring a position of the transforming disk 450 to original position, and a spacing portion 470 for maintaining a space of the transforming disk 450.
And the wire installed at the hooking portion of the transforming disk 450 is connected with a lever (not shown) disposed at a handle.
When changing speed of the bicycle using the above-mentioned apparatus, the wire connected to the lever rotates the transforming disk by operation of the lever. And, the pawl controlling ring is rotated to a proper position, such that the pawl is engaged with the ratchet-teeth formed at the inner circumference of one of the sun gears so as to transmit the rotational force, and thus the planetary gear engaged with the outer circumference of the sun gear, thereby achieving the speed changing. Herein, if a larger sun gear is selected, the bicycle is in a high speed state, and if a small sun gear is selected, the bicycle is in a middle speed state, and if none of the sun gears is selected, the bicycle is in a low speed state.
Meanwhile, when an uphill road running is started while the bicycle is driven at high speed, lower gear ratio of the apparatus may be selected to reduce the speed of by bicycle so as to increase the rotation torque. At this time, following problems are occurred. That is, when trying to operate the lever and rotate the pawl to a deceleration position, since the pawl continuously pushes the ratchet teeth in a state of being strongly engaged with the ratchet teeth formed in the inner circumference of the sun gear, it is not easy to rotate the pawl controlling ring. Only after an excessive force to a degree that at least the pawl goes over an inclination surface of the ratchet teeth is applied, the gear shifting can be achieved.
When the bicycle is driven at the downhill road with less pedaling force, the engagement between the pawl and ratchet teeth is released and the gear shifting can be achieved with small force, and thus, though the shifting cannot be achieved due to strong pedaling force at the uphill road running, it does not matter much.
However, in case that the above-mentioned transmission is applied to an electrical bicycle in which an electric motor is utilized as a driving means, since strong force is always exerted between the pawl and the ratchet teeth which are engaged with each other, it is not easy to perform the gear shifting. Therefore, in case that the gear shifting is performed by operating an electrical device such as an electrical switch which generates relatively small driving force, it is further difficult to achieve the gear shifting.
Meanwhile, in Japanese Patent Publication No. Hei 10-96453, it is described that the gear shifting can be achieved even though the pawl is strongly engaged with the ratchet teeth of the sun gear. In the document disclosed, a small electric motor for controlling the gear shifting is provided so as to rotate the pawl. Herein, if rotational force for rotating the pawl is higher than output of the electric motor, wheel driving force derived from a driving force transferring portion is transferred to the pawl controlling ring, thereby achieving the shifting. Therefore, since the wheel driving force is actually used in the above-mentioned document though the small electric motor is used, it is hard on the components and also it loses part of the driving force. Further, since the mechanism for transferring the driving force from the driving force transferring portion to the pawl-controlling ring is so complicated, it is difficult to embody the mechanism actually.